1. Field of the Invention
The invention relates to a fuel injection nozzle of an internal combustion engine. More specifically, the invention relates to a technology in which a fuel injection nozzle induces cavitation to atomize injected fuel.
2. Description of the Related Art
The atomization of fuel injected from a fuel injection nozzle is effective for reducing the amount of pollutants in exhaust gas, and improving fuel efficiency. Japanese Patent Application Publications No. 2003-206828 (JP-A-2003-206828) and No. 2004-316598 (JP-A-2004-316598) describe that cavitation is induced in fuel in a fuel injection nozzle, and the fuel mixed with cavitation bubbles is injected.
In the technology described in the publication No. 2003-206828, an edge protrusion that protrudes into the flow of fuel is formed at the edge of a valve seat. The flow of fuel is separated from the valve seat by the edge protrusion. As a result, cavitation is induced. The edge protrusion is disposed immediately upstream of an injection hole. Therefore, cavitation bubbles generated by the edge protrusion flow into the injection hole, along with the fuel.
In the technology described in the publication No. 2004-316598, a plurality of injection-hole inlet passages, which extends from a valve seat, is formed in a nozzle body. The downstream ends of the injection-hole inlet passages are connected to each other by a communication passage. A plurality of injection-port outlet passages is also formed in the nozzle body. The injection-port outlet passages extend from the communication passage to respective injection outlets formed on the outer surface of the nozzle body. When the fuel flows from the valve seat to the injection outlets through the injection-hole inlet passages, the cavitation is induced in the injection-hole inlet passages. Further, the fuel that flows in the communication passage collides with the fuel that flows out of the injection-hole inlet passages at the inlet portions of the injection-hole outlet passages. The collision energy promotes the disturbance of the flow of fuel in the injection-hole outlet passages, and accordingly promotes the mixing of the cavitation bubbles into the flow of fuel.
However, in the technology described in the publication No. 2003-206828, because the cavitation is induced near the injection hole, the fuel may be injected before the fuel and the cavitation bubbles are sufficiently mixed with each other. In the technology described in the publication No. 2004-316598, because the injection-hole inlet passages extend directly from the valve seat, the occurrence of cavitation in the injection-hole inlet passages is greatly influenced by the flow passage area of a space between the valve seat and the needle valve. More specifically, when the needle valve has just moved away from the valve seat, the flow passage area of the space between the valve seat and the needle valve is small. Thus, the flow passage area of the space between the valve seat and the needle valve only slightly differs from the flow passage area of the injection-hole inlet passages. Therefore, when the fuel flows from the valve seat into the injection-hole inlet passages, the pressure of the fuel only slightly decreases. As a result, the cavitation may not be sufficiently induced in the injection-hole inlet passages.
Thus, the above-described conventional fuel injection nozzles need to be improved to sufficiently atomize the fuel.
US 2006/0097082 discloses a fuel injection nozzle with a needle valve and a valve seat. Fuel flows through a passage to a plurality of injection outlets. A rip causes in the exit cavity a cavitating flow region which enhances the atomization of the fuel.